The severity of the AIDS epidemic in the developing world combined with the limited resources that some of these countries have available for health care render the need of an AIDS vaccine more urgent every day. When tested in Rhesus macaques, the candidate vaccines developed thus far, evaluated predominantly via the intramuscular route, do not protect from chronic infection but provide a reduction in the viremia set point and a delay of progression to AIDS. The control of viremia and the length of disease-free infection depend on the model of infection used for the vaccine evaluation in non-human primates. As substantial virus replication occurs in the gastrointestinal tract in addition to the lymphoid organs, the ability of vaccines to induce immunity both in mucosal and systemic compartments may be required for prevention of HIV infection and AIDS. We have established vaccination regimens that stimulate mucosal responses with an SIV DNA vaccine, which consists of a single plasmid carrying an SIV proviral genome that produces noninfectious particles, whether the vaccination occurs via the rectal or nasal route. We have the appropriate tools to measure SIV-specific IgA levels in mucosal secretions, mucosal cell-mediated responses, and SIV-specific systemic responses. As a consequence, we believe that we are uniquely placed to determine the effectiveness of oral DNA vaccination and how stimulation of virus-specific mucosal responses can affect the efficacy of a HIV/SIV vaccine. Exploring vaccination regimens administered via the oral route may be important to establish regimens capable of providing substantial control of viral replication in the gastrointestinal tract. Towards this goal we propose 1. To evaluate whether different doses of a DNA plasmid expressing the Hepatitis C Virus 70 kD E2 Envelope protein and combined with PLG micro particles stimulate significant anti- Hepatitis C Virus 70 kD E2 immune responses systemically and mucosally when administered orally to Rhesus macaques. 2. To evaluate whether a liposome or a micro particle formulation of a DNA-MVA SIV vaccine stimulates broader mucosal and systemic responses after oral administration. 3. To evaluate which of the two above regimens provides the best protection from vaginal SIV challenge. 4. To evaluate whether the better of the two above regimens can be further improved in its protection from progression to AIDS by the simultaneous administration of a similarly formulated DNA-MVA intradermal immunization. Project Narrative: AIDS vaccines may need to engender a substantially greater level and breadth of immunity than other vaccines. It is important to explore approaches that may enhance the quality and not simply the quantity of the immune response because an efficacious vaccine will have to provide protection at times other than the peak of the immune response. The simultaneous presence of both mucosal and systemic immunity may be important in preventing the establishment of a chronic HIV/SIV infection and in controlling disease progression if infection occurs. Oral vaccination may be best suited at providing virus-specific responses that reside in the gastrointestinal tract where a significant amount of HIV and SIV replication occurs during the infection. Toward this goal we intend to investigate strategies that should maximize the quality and quantity of immune responses produced by our SIV DNA vaccine in all the compartments of the immune system. The objective of the studies proposed here is to evaluate which of two different formulations of the DNA/MVA vaccine provides the most diverse immune responses when administered orally and the most significant protection from disease progression after viral challenge. Antiviral immunity in the genital tract is not only critical because of the role that these responses can play at the time of sexual exposure to HIV but also because of the role that these responses may play in preventing vertical transmission. The results of such studies should be highly valuable for AIDS vaccine development.